Allina Health hospital nurses voted Monday night to reject a contract offer from their employer, increasing the likelihood that their walkout over health benefits, staffing and safety concerns will go down as the longest nursing strike in Minnesota history.

While the Minnesota Nurses Association had not recommended a “no” vote, many nurses said they felt Allina’s latest offer was too similar to one they rejected in August, and to the terms their union negotiators rejected during last-ditch negotiations in September to avert a strike.

A new sign reading “New Lipstick, Same Pig” appeared at the picket line outside Allina’s Abbott Northwestern Hospital in Minneapolis Monday morning, foreshadowing the vote result that the union announced at 10:30 p.m. in St. Paul.

While she declined to provide exact results, MNA executive director Rose Roach called the vote margin “resounding” and said it sent a clear message from front-line nurses to go back to the bargaining table. “Each of them voted with their conscience, and with their patients and their families in mind,” she said.

The results mean that strikes will continue at Abbott as well as United Hospital in St. Paul, Mercy Hospital in Coon Rapids, Unity Hospital in Fridley and the Phillips Eye Institute in Minneapolis.

More than 4,000 nurses have been on strike for 29 days, since Labor Day, after a one-week walkout in June. The state’s longest nursing strike, in 1984, lasted 38 days.